BSTJ 18: 4. October 1939: Abstracts of Technical Articles from Bell System Sources .

Abstracts of Technical Articles from Bell System Sources

Recent Observations on the Relation between Penetration, Infection and
Decay in Creosoted Southern Pine Poles in Line} C. H. Amadon.
The relation between poor penetration and decay, and the necessity
for rational and adequate penetration requirements in treating
specifications, are now fairly well understood by producers and users
of creosoted southern pine poles. The purpose of this brief paper is
to supplement the information presented in the Proceedings for 1936
and 1937 on the behavior of these poles in line under actual service
conditions.

Tarnish Studies. The Electrolytic Reduction Method for the Analysis
of Films on Metal Surfaces.'^ W. E. Campbell and U. B. Thomas.
A method is described for analysis of tarnish films on metals by
electrolytic reduction at the cathode. Its suitability is demonstrated
for the rapid and accurate measurement of oxide films on copper
varying in average thickness from monomolecular layers to 1000 A.
It is shown to be useful for reduction of mixed oxide-sulfide films on
copper and silver. The method is used to measure the oxide films
on freshly reduced copper after one-half hour's exposure to oxygen
or air. Such films are shown to be 10-20 A thick. A thicker film,
measuring 30-70 A is found to be produced by abrasion of copper in
air, water, benzene or toluene. Adaptations and modifications are
discussed which give wide analytical application to the method.

An Electrochemical Study of the Corrosion of Painted Iron.^ H. E.
Haring and R. B. Gibney. The corrosion protective value of
approximately 50 different paints was determined by means of an
electrochemical method which has been previously described. This
determination involved the measurement of the change in the potential
of the painted iron with time when wet with water for 24 hr. or less.
It was found that the interpretation of the time-potential curves
which were automatically plotted by a recording vacuum tube elec-
trometer, was facilitated if the test was conducted in a nitrogen
atmosphere. The results obtained with the electrochemical or
potentiometric method compared favorably with those obtained in a

^ Proc. American Wood-Preservers' Association, 1939.
* Electrochemical Society Preprint 76-25.
' Electrochemical Society Preprint 76-24.

742

ABSTRACTS OF TECHNICAL ARTICLES 743

one-year outdoor exposure test. Such differences as were found were
shown to be due either to deterioration or improvement in the paint
film as the result of weathering.

Characteristics of Modern Alicrophones for Sound Recording.^ F. L.
Hopper. Factors influencing the choice of a microphone for sound
recording are considered. The characteristics of a new miniature
condenser transmitter and ampHfier, as well as a number of other
types of microphones now in use, are included.

Cold-Cathode Gas-Filled Tubes as Circuit Elements^ S. B. Ingram.
The application of electronic devices to the local systems plant is
still in its infancy. One of the first of these devices to receive extensive
use is the cold-cathode gas-filled tube. As a sensitive relay it is
beginning to make its appearance in a number of telephone control
and signaling circuits, being best kxiown for its use in the standard
four-party subscriber set where its rectifying property enables it to
discriminate between positive and negative polarity for selective
ringing. Compared with other types of vacuum tubes the cold-
cathode tube has the advantages that it operates without cathode
heating power, has the ability to start immediately when a signal is
applied, and does not deteriorate when not passing current. These
advantages make it particularly suitable for use in telephone circuits
where intermittent service is common and long life and economical
operation are required.

The paper describes the structure and electrical characteristics of
cold-cathode tubes. Their properties as circuit elements are then
illustrated in a number of typical basic circuits.

Inductive Coordination with Series Sodium Highway Lighting Circuits.^
H. E. Kent and P. W. Blye. This paper describes the wave-shape
characteristics of the sodium-vapor lamp and discusses the relative
inductive influence of various series circuit arrangements in which
such lamps are employed. A method is outlined by means of which
the noise to be expected in an exposed telephone line may be estimated.
Measures are described which may be applied in the telephone plant or
in the lighting circuit to assist in the inductive coordination of the
two systems. These measures need be considered only when a con-
siderable number of lamps is involved, since noise induction is negligible

* Jour. S.M.P.E., September 1939.
^Etec. Engg., July 1939.
« Elec. Engg., July 1939.

744 BELL SYSTEM TECHNICAL JOURNAL

when there are only a few lamps as, for instance, at highway inter-
sections.

A Cardioid Directional Microphone.'^ R. N. Marshall and W. R.
Harry. A microphone is described which has uniform directivity
over a wide frequency range. This is made possible by placing in a
single instrument a dynamic type pressure microphone element and a
ribbon type "velocity" element, and electrically equalizing the out-
puts before combination. The resultant directional pattern is a
heart-shaped curve or cardioid, giving a fairly wide pick-up zone in
front and a substantial dead zone at the back of the instrument.
Because of the unusually rugged ribbon employed, the new microphone
is much less susceptible to wind noise than ordinary ribbon types.
Housed in an aluminum case, the microphone weighs only 3J lbs.
High output level, low impedance, and high quality, together with
the excellent directivity, promise to make the cardioid microphone an
important tool for the motion picture sound engineer.

Fractional-Frequency Generators Utilizing Regenerative Modulation.^
R. L. Miller. By the application of the principle of regeneration to
certain modulation systems, a generator of submultiple or other
fractional -frequency ratio may be obtained.

A simple example is obtained by considering a second-order modu-
lator whose output is connected back to a conjugate input by means
of a feedback loop including an amplifier and a selective network.
If an input frequency /o is applied, it is found that a frequency com-
ponent /o/2 appearing in the feedback path will modulate with the
applied frequency to produce sidebands of /o/2 and 3/o/2. The net-
work and amplifier, being especially efficient for the frequency /o/2
and having a gain higher than the modulator loss, will reinforce this
component causing it to build up to some steady-state value. Similar
processes are possible by which greater submultiple ratios may be
obtained.

Since the output wave is obtained by a modulation process involving
the input wave, it will appear only when an input is applied and then
bears a fixed frequency ratio with respect to it. Experiments show
that the ability of the generator to produce a fractional frequency is
independent of phase shift in the feedback path. Circuits are possible
in which the amplitude of the fractional-frequency wave will bear a
linear relation to the input wave over a reasonable range and at the

^ Jour. S.M.P.E., September 1939.
^Proc. Z.iJ.E., July 1939.

ABSTRACTS OF TECHNICAL ARTICLES 74S

same time maintain a constant phase angle between the two waves.
Typical circuits are discussed which make use of copper oxide as the
modulator elements.

Seasonal Cosmic-Ray Effects at Sea Level.^ R. A. Millikan,
H, V. Neher and D. O. Smith. By sending a Neher self-recording
electroscope in a 10-cm lead shield repeatedly on a slow Norwegian
steamer over the route Vancouver-Los Angeles, around South America
and return to Los Angeles and Vancouver, we find (1) as heretofore
an equatorial dip measured from Los Angeles of seven per cent on the
western side of South America, eight per cent on the eastern side;
(2) no measurable seasonal effect, or winter-summer differences, at all
in the voyage from Los Angeles to the Straits of Magellan; (3) as
heretofore constancy in cosmic-ray intensity in summer and fall,
within the limits of uncertainty imposed by fluctuations estimated
at not over one per cent, on the voyage between Los Angeles and
Vancouver; (4) but in winter and spring an increase of as much as
two or three per cent between Los Angeles and Vancouver. This is
interpreted as the atmospheric-temperature effect earlier studied by
Hess, Compton, and their respective collaborators.

Some Engineering Considerations in Loading Circuits.^'^ J. A.
Parrott. This paper describes the various loading arrangements
used on toll entrance and intermediate cable circuits and discusses the
transmission benefits obtained by loading and some of the important
problems in the consideration of loading railroad entrance and inter-
mediate cables. In addition to voice frequency loading, loading for
the lower frequency carrier systems such as the Type H is also
discussed.

The Formation of Metallic Bridges between Separated Contacts.^^
G. L. Pearson. Low resistance bridges were formed between gold,
steel and carbon electrodes having separations of 2-70 X 10~^ cm by
applying voltages less than the minimum sparking potential. For a
given pair of electrodes the field required to form the bridges is a
constant and is 5-16 X 10^ volts per centimeter. Measurements of
the temperature coefllicient of resistance of the bridges identify therfi
as consisting of the material of the electrodes. A study of their re-
sistance as a function of the displacement of one of the electrodes
shows that they may be pulled out as well as crushed. At voltages

^Phys. Rev., September 15, 1939.

loProc, Assoc. Amer. R.R., Telegraph and Telephone Section, April 1939.

"PAys. Rev., September 1, 1939.

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746 BELL SYSTEM TECHNICAL JOURNAL

less than those required to form the bridges, field currents exist.
These increase rapidly as the field is raised and attain a value around
10-'° ampere before the bridges are formed. Calculation of the
maximum electrostatic stress on the electrodes at the time of break-
down gives a value 0.05 to 0.0005 times the tensile strength of the
electrode material at room temperature. The field is locally higher
than that calculated because of surface roughness and the tensile
strength is probably lowered by the local heating known to accompany
field currents. The data therefore indicate that electrostatic force
pulls material from the electrodes to bridge the gap.

Measuring Transmission Speed of the Coaxial Cable}^ J. F. Wentz.
Time of transmission of carrier currents over high speed lines is dis-
cussed. A method of measuring this time delay as used on the
1000-kc system of the New York-Philadelphia coaxial cable is de-
scribed and the results are given for the television band transmitted
over it experimentally.

i> Bell Labs. Record, June 1939.